1. Field of Invention
The invention relates to a fan system, a control device of a fan system and a control method of a fan system. In particular, the invention relates to a fan system, a control device of a fan system and a control method of a fan system, which can start a fan in a lower rotation speed.
2. Related Art
In general, electronic systems are equipped with a fan system for heat dissipation. The fan system usually has a control device and at least one fan, and the control device can adjust the rotation speed of the fan according to the actual working status of the electronic system. For example, when an external system has a commonly used CPU (Central Processing Unit), the produced heat energy is relatively high. If a fan system is used in this external system, it can adjust the rotation speed of the fan through the control device in order to meet the heat dissipating requirement. On the contrary, when the CPU is in an idle state, the rotation speed of the fan can decrease relatively such that the energy may be saved.
FIG. 1 is a block diagram showing a conventional control device 10 of a fan system, which is cooperated with an external system 1. Referring to FIG. 1, the control device 10 includes a rotation speed controlling unit 11 and a driving unit 12, which is typically a driving chip. The rotation speed controlling unit 11 has a power supply source coupled to an exterior voltage source V, and a signal input terminal for receiving a target rotation speed controlling signal 101 outputted by the external system 1 and producing a rotation speed controlling signal 102 according to the target rotation speed controlling signal 101. The driving unit 12 controls a rotation speed of a fan 13 according to the rotation speed controlling signal 102. In general, the voltage of the rotation speed controlling signal 102 is inversely proportional to the rotation speed of the fan 13. That is, as the voltage of the rotation speed controlling signal 102 decreases, the rotation speed of the fan 13 increases.
When the control device 10 is initially started, the target rotation speed controlling signal 101 may not reach the desired voltage level immediately since the external system 1 still performs the initialization operation. Thus, the control device 10 may output the rotation speed controlling signal 102 with a low voltage, which leads to the fastest rotation speed of the fan 13. In this situation, the starting current of the fan is excess. In addition, if the fan 13 has problems (e.g. it may be stuck by something) and the problems are then be removed, the control device 10 should be restarted. In this situation, the rotation speed controlling signal 102 can not be outputted immediately, too, so that the fan 13 operates at the fastest rotation speed. Therefore, the starting current of the fan is also excess. The above mentioned situations both lead to the energy waste and the increasing temperature of the fan.
Therefore, it is desirable to provide a fan system, a control device of a fan system and a control method of a fan system, which can use lower rotation speed to start or restart a fan so as to solve the above-mentioned problems.